#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=1e6+100;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL a[maxn],dp[maxn];
map<LL,LL>map1;
int main(void)
{
  ///cin.tie(0);std::ios::sync_with_stdio(false);
  LL n;n=read();
  for(LL i=1;i<=n;i++){
    a[i]=read();
  }
  map1[a[1]]=1;
  for(LL i=2;i<=n;i++){
     if(map1.count(a[i])){
         dp[i]=max(dp[i-1],dp[map1[a[i]]]+1);
     }
     else dp[i]=max(dp[i],dp[i-1]);
     map1[a[i]]=i;
  }
  LL ans=0;
  for(LL i=2;i<=n;i++){
    ans=max(ans,dp[i]);
  }
  printf("%lld\n",ans);
return 0;
}
